Reactivity studies of the zirconium alkylidene complexes [η5-C5H3-1,3-(SiMe2CH2PPri2)2]Zr=CHR(Cl) (R = Ph, SiMe3)

Reactivity studies of the zirconium alkylidene complexes [P2Cp]Zr=CHR(CI) (1a, R = Ph; 1b, R = SiMe3; [P2Cp] = eta(5)-C5H3-1,3-(SiMe2CH2PPr2i)(2)) are described. The reaction of 1 with ethylene follows second-order kinetics to give the ethylene complex [P2Cp]Zr(eta(2)-C2H4)CI (2), the structure of which was determined by X-ray crystallography. Addition of acetone to 1 generates the alkene RCH=CMe2, although the anticipated Zr oxo species could not be isolated from this reaction. An insertion of CO into the Zr=C bond of 1 yields the ketene complex [P2Cp]Zr(eta(2)-C,O-OC=CHR)CI (3), while the reaction with tert-butyl isocyanide gives the analogous ketenimine complex [P2Cp]Zr(eta(2)-C,N-(BuNC)-N-t=CHR)CI (4). The structure of ketene 3a (R = Ph), determined by X-ray diffraction, exhibits the E geometry, with the position of the ketene unit with respect to the ancillary [P2Cp] ligand being opposite to that in the configuration of the precursor alkylidene la. The ketene complex 3 reacts with ethylene to give [P2Cp]Zr(eta(2)-C,O-CH2CH2C(O)=CHR)CI (5). The molecular structure of 5b (R = SiMe3) was obtained by X-ray diffraction and reveals a five-membered zirconaoxacycle arising from the insertion of ethylene into the Zr-C bond of the ketene, which is subsequently coordinated to the metal as an enolate ligand. 5 undergoes a final insertion reaction with CO to give the asymmetric eta(2)-acyl-ylide complex. For each reaction detailed above, dissociation of a labile pendant phosphine donor provides an open site for reactivity.